The present invention relates to motion correction in medical image data, and more particularly to magnetic resonance imaging (MRI) based respiratory motion correction for PET/MRI image data.
Modern positron emission tomography (PET) imaging techniques have led to widespread use of PET, including in oncology, neuroimaging, cardiology, and pharmacology. However, PET image data often suffers from image degradation due to patient motion during the PET image data acquisition. Motion can occur due to normal breathing, heartbeat, and gross patient movement during the image acquisition. Among the different types of motion, respiratory motion typically has the largest impact on thoracic and abdomen imaging due to its large magnitude and the larger variation of breathing patterns.
Various techniques have been used to minimize the effects of respiratory motion in image acquisition, including breath holding, respiratory gating, and advanced reconstruction techniques. Due to the long acquisition time of PET (typically one to three minutes per bed position), breath holding techniques are difficult to apply. Respiratory gating strategies divide a breathing cycle into several phases, which can be measured by a navigation signal (e.g., using a respiratory belt). List-mode PET data are then clustered into different breathing phases based on the navigation signal to “freeze” to motion. However, such respiratory gating techniques assume that respiratory motions in the same breathing phase are identical across different breathing cycles, which is not true due to the fact that breathing motion patterns can be irregular, especially when the patient is under stress, anxiety, and/or pain.
PET/MRI image acquisition systems allow for simultaneous acquisition of PET and MR data with accurate alignment in both temporal and spatial domains. However, 4D MR image data with a high spatial resolution typically has a very low temporal resolution, which limits its usefulness for motion estimation. Recently, some techniques have been proposed to take advantage of simultaneous PET/MRI acquisition for PET respiratory and cardiac motion correction. However, due to the tradeoff between spatial and temporal resolution of MR imaging, all of the proposed methods rely on gating for 3D MRI acquisition. Accordingly, these methods suffer from the same drawbacks as other respiratory gating techniques.